The present invention relates to a method, computer program product, and device for processing projection images, and more specifically, to a method, computer program product, and device for processing noise within image data of projection images.
Conventionally, medical image information generated by diagnostic medical imaging devices such as diagnostic X ray devices, CT X ray devices, magnetic resonance imaging devices (MRI devices), and the like are used in performing medical procedures such as medical diagnostics and treatment. Medical image information is processed to obtain an image which can be displayed three-dimensionally, and the image is viewed for the purpose of diagnosis or treatment. Two types of methods for displaying three-dimensional images are described below.
One such method extracts from medical image information a region that is to be displayed, such as an internal organ and the like, to generate an image of the surface of the organ or the like from the image data of the extracted region (hereinafter referred to as “surface display method”). Another method is the volume rendering method. In the surface display method and volume rendering method, volume data including three-dimensional pixels (voxels) are created using medical image information (three-dimensional data formed by a collection of two-dimensional cross-sectional images (slices)). In the surface display method, a display subject (e.g., bone or organ) is extracted from volume data as a region-of-interest, and only this region-of-interest is viewed.
U.S. Pat. No. 5,793,375 discloses an example of a method for extracting a region-of-interest. In order to extract a region-of-interest, voxel data, which include voxels having tone values, are first binarized based on predetermined threshold values so as to generate binarized voxel data. Thereafter, a light beam is extended from each pixel to the binarized voxel data, and the length of the light beam required to reach a voxel (region-of-interest voxel) which has a value of “1” is determined. A depth image is created based on the lengths of the light beams corresponding to the pixels. The coordinates on the surface of the display subject are calculated backward from the depth image. An image is created for displaying the surface of a subject by determining and projecting a planar normal line based on the voxel value of specific voxel data and the voxel value of adjacent voxel data.
In volume rendering, a light beam is directly projected on volume data to create an image. A particularly often used method is maximum intensity projection (MIP). In MIP, voxel data is prepared similarly to the previously mentioned surface display method, and an optical path is set through the voxel data. Then, a MIP image which has been generated based on the voxel data having maximum values on the optical path (pixel value of each pixel of the medical image information) is displayed on the two-dimensional plane of the projection surface at a right angle to the optical path.
There may be occasions when noise is included in the medical image information forming the basis of the display image. In the surface display method, when such noise exceeds a threshold value, the noise may be erroneously recognized as the region-of-interest. Accordingly, the displayed image may not meet the requirements of the user. In MIP, noise contained in the medical image information may also be erroneously recognized as maximum data on the optical path. For example, although a user may desire an MIP image MP1, which does not include noise as shown in FIG. 1, the actual displayed MIP image MP2 may include dot-like noise N, as shown in FIG. 2. Such noise may hinder accurate diagnosis and treatment.